When to Prune Dead Lilac Flowers

Deadheading

• The lilac shrub generally blooms for several weeks in the spring. Once a flower cluster fades, cut the stem back to the first or second set of leaves. This encourages new growth during the summer. As the rest of the flowers continue to fade, repeat the pruning process with each flower stem. Lilacs set buds the previous year for blooms the following year. If you wait until summer or fall to prune the dead flowers, next year's blooms will be lost and your lilac shrub will not flower the following spring.

Seed Pods

• The lilac sets seed once the blooms fade. This means the lilac shrub devotes much of its energy to producing the seeds instead of producing buds for next year. Deadheading the shrub as soon as the flowers are spent forces the plant to put the energy into bud production instead of seed pods. If you do want seeds from the lilac, leave one spent flower cluster for seed development and remove the rest.

Window of Opportunity

• The plant sets buds for the following season approximately one month after the last flower fades from the lilac shrub. If your spent flowers are still on the shrub in late July, check the plant before removing the dead flowers. There may already be bud growth on the flower stems. If you don't mind losing a few flower sprays during the spring, it will not harm the shrub to cut the spent flowers from this year's growth so late in the season.

Rejuvenation

• Some lilac cultivars can grow to enormous heights, 20 feet or more, for a shrub. Pruning brings the shrub back into a manageable size. Rejuvenation is another reason for pruning the lilac when the flower clusters die. It may seem harsh, but a hard pruning protects the lilac from pests and disease. Cut back about 1/3 of the largest trunks to about 4 inches above the soil line. New sprouts will shoot up during the current growing season. The remaining stalks will bloom in the spring. Repeat the process with another 1/3 of the remaining canes the following spring. The third spring pruning will result in new canes for the entire shrub. Your lilac blooms should remain plentiful.